1. Field of the Invention
The present invention relates to a method and a printing technology machine for controlling the color in printing technology machines, wherein color measured values are measured without a UV filter and are converted through the use of a computer to color measured values measured with a UV filter, and vice versa, and wherein the color measured values measured without/with a UV filter can be recorded through the use of a color measurement instrument on a substrate.
During the production of printed products, the print quality must be continually checked during production. In order to do that, sample sheets are taken from the printing machine at least at specific time intervals, and are measured through the use of a color measurement instrument. The color measured values recorded in that way are then compared with the original. If any intolerable discrepancies occur during that process, then the color in the printing machine must be changed in such a way that the substrates that are produced are once again as close as possible to the original. So-called optical brighteners are very widely used in modern substrates. However, those optical brighteners influence the color impression since they convert the UV components of the illuminating light to visible light in the short-wave range. Visually, the substrate thereby appears to be slightly bluish, and therefore whiter. However, that influences the overall color impression. When color measurements are then carried out for quality control purposes through the use of a color measurement instrument on substrates such as those with brighteners, the measurement result is significantly dependent on the UV component of the illuminating light, and the effect of the optical brightener. All color measurement instruments which operate without a UV filter have a significant UV component in the illuminating light, as a result of which that problem occurs widely with color measurement instruments. A further problem results from the fact that the UV components in the illuminating light may fluctuate. In consequence, the measured values vary in a corresponding manner, which in turn adversely affects the comparability of measurements which have been carried out using different color measurement instruments and different UV components. Particularly major discrepancies occur when one measurement instrument is equipped with a UV filter while the other operates without a UV filter. In order to make measurements such as those comparable, the color measured values recorded without a UV filter and those recorded with a UV filter must, however, be made comparable in some way. In this application, a UV filter means a UV filter which suppresses the UV component and allows only the spectrum of the light outside the UV spectrum to pass. UV filters such as those are also referred to as UV cut filters, and those two expressions are used synonymously in the instant application.